CN113518853B

CN113518853B - Internal combustion engine

Info

Publication number: CN113518853B
Application number: CN202080017593.6A
Authority: CN
Inventors: V·I·拉克什米纳拉西姆汉; T·L·巴拉苏布拉曼尼亚; K·维蒂林格
Original assignee: TVS Motor Co Ltd
Current assignee: TVS Motor Co Ltd
Priority date: 2019-03-13
Filing date: 2020-02-14
Publication date: 2023-10-24
Anticipated expiration: 2040-02-14
Also published as: CN113518853A; WO2020183486A1; EP3938629A4; EP3938629A1; JP2022520881A

Abstract

The present subject matter relates to a camshaft assembly for an internal combustion engine for providing mechanically variable valve timing. The camshaft assembly (200) includes a mechanical phasing assembly (230) disposed adjacent to one of the at least one intake flange (220) and the at least one exhaust flange (225). The at least one radially preloaded mass member (235) is configured to perform a phase shift of at least one of the intake flange (220) and the exhaust flange (225) relative to the driven sprocket (205) as a function of a rotational speed of the camshaft assembly (200). An axial load member (245) preloaded in an axial direction is disposed adjacent to the mass member (235) to apply an axial load thereto. The inventive subject matter improves valve opening and closing time variation to meet intake and exhaust demands of an engine at all operating speeds.

Description

Internal combustion engine

Technical Field

The present subject matter relates generally to an Internal Combustion (IC) engine for a motor vehicle. More specifically, the present subject matter relates to a camshaft assembly for an internal combustion engine that provides mechanically variable valve timing.

Background

Internal Combustion (IC) engines are used to convert chemical energy into mechanical energy through the combustion of an air-fuel mixture. The thermal energy generated as a result of combustion of the air-fuel mixture is used to provide motion to one or more reciprocating pistons within the cylinders. One or more reciprocating pistons transfer this reciprocating motion, resulting in rotational motion of one or more crankshafts coupled thereto by connecting rods with a slider-crank mechanism. The cylinder head generally includes at least one intake port and at least one exhaust port that respectively allow an air-fuel mixture to enter from the combustion chamber and allow combustion gases to exit from the combustion chamber. In this operation, the precise movement and timing of the opening and closing of the inlet and outlet ports of the combustion chamber is critical to the accurate performance of the IC engine.

Typically, such opening and closing of the inlet/outlet ports is controlled by various components present on the cylinder head and cylinder bore, and the opening and closing of the valves is driven by one or more camshafts driven by one or more crankshafts through a camshaft transfer system. The camshaft includes cam lobes that control the orifice opening and the duration of the orifice opening. One of the biggest drawbacks of many commuter motor vehicle engines is the use of fixed timing to close and open the orifice (through the valve), so these engines operate in a suboptimal manner. For example, a fixed timing of the valve at a higher speed sets the opening time to an optimal setting, while a higher valve opening is desired. The intake valve may close late using the inertia of the intake air. However, such later opening of the valve at lower engine speeds can affect the volumetric efficiency of the engine. Therefore, even if set to an optimal setting, the fixed timing of valve opening can affect engine performance over a particular speed range. Various electrical, electromechanical, mechanical and hydraulic means for achieving cam phasing are known in the art. For example, cam phasing, cam variation, etc. are some of the techniques used in the prior art. For example, cam phasing is one of the techniques to provide a phase difference of one cam lobe from another cam lobe to achieve variable valve opening.

Drawings

The detailed description is described with reference to the accompanying drawings.

FIG. 1 illustrates a side view of an exemplary Internal Combustion (IC) engine according to an embodiment of the inventive subject matter.

FIG. 2 illustrates an exemplary cross-sectional view of an IC engine, the cross-sectional view taken along axis W-W'.

Fig. 3 (a) shows a perspective view of a camshaft assembly according to an embodiment of the inventive subject matter.

Fig. 3 (b) shows another perspective view of the camshaft assembly with selected parts thereon according to the embodiment of fig. 3 (a).

Fig. 3 (c) shows a radial cross-sectional view of camshaft assembly 200 taken along axis U-U'.

Fig. 4 depicts the mass member in the first state and the second state according to the embodiment of fig. 3.

Fig. 5 (a) shows a cross-sectional view of a camshaft assembly according to an embodiment of the inventive subject matter.

Fig. 5 (b) shows another cross-sectional view of a camshaft assembly according to an embodiment of the inventive subject matter.

FIG. 6 illustrates an exploded view of a camshaft assembly according to an embodiment of the present subject matter.

FIG. 7 illustrates a detailed cross-sectional view of a camshaft assembly according to an embodiment of the inventive subject matter.

Detailed Description

Typically, cam phasing/modification enables the engine to operate beyond its suboptimal performance. For example, if the intake valve is advanced during a lower RPM, the intake valve experiences early closing, minimizing backflow during the compression stroke, thereby improving volumetric efficiency and torque at a lower RPM. Furthermore, at higher RPM, phasing may be performed on the intake valve, which results in retarded/retarded closing of the intake valve, thereby taking advantage of the momentum of air entering the intake manifold at high speeds for scavenging. Similarly, the opening and closing of the exhaust valve may be advanced or retarded by cam phasing. Moreover, cam phasing may be accomplished on both the intake and exhaust valves.

Typically, to perform cam phasing/changing, various electrical, electromechanical and hydraulic devices are used, such devices being complex and not cost effective. For example, solenoids or slide pins, etc. are required, which are accommodated in the vicinity of a camshaft portion that requires a large space on an already compact cylinder head region. Furthermore, it is important for a two-or three-wheeled vehicle to be as compact as possible to enable packaging in a small space and to allow easy access to the various parts of the power system for timely repair and repair with simple tools without the need to disassemble the power system from the vehicle. Furthermore, such electric/electromechanical or hydraulic systems comprise an electric or hydraulic drive which is powered by an on-board battery and controlled by a control unit. Furthermore, the addition of a control module like a controller increases the cost of the system and the motor, for example, a stepper motor that causes phasing to make the engine bulky, especially the cylinder head portion. In some other solutions known in the art, sliding mechanisms for engaging and disengaging various rocker arms according to speed are suggested. Even in such systems, an externally controlled slider is required and a motor or the like is used to control the slider movement, making the system more expensive and bulky. Thus, additional systems are needed and those systems also consume battery power. Furthermore, the functional characteristics of the electrical and mechanical systems are affected by changes in engine temperature, for example during cold start or at high temperatures.

Furthermore, mechanical phasing systems are known in the art to be able to perform cam phasing in response to changes in engine speed/RPM. In general, mechanical phasing systems can be used in compact vehicles (like two-wheeled or three-wheeled vehicles with compact engine layouts). Moreover, such mechanical phasing systems provide cost effectiveness as they can operate without any electrical/hydraulic control. However, such systems are not anyway and tend to fail when the phase angle increases. For example, in mechanical systems using centrifugal force for cam phasing, cam phasing occurs abruptly even before a desired speed is reached due to force components acting on the phasing device, such as centrifugal force components/inertial components. Such problems are prominent in vehicles that use a single camshaft to control both the intake and exhaust valves because the torque of the camshaft is higher and the operating speed of the camshaft is also higher. In consideration of the case where the user suddenly accelerates, a sudden increase in the rotational speed/velocity of the camshaft occurs, which causes a sudden increase in centrifugal force, which causes an increase in centrifugal component, resulting in sliding. Furthermore, even in systems employing roller bearings, such premature phenomena may occur due to centrifugal forces. Thus, in such systems, cam phasing occurs at an undesirable rate, affecting the performance of the system due to the opening/closing of the valve under undesirable conditions, and this may also lead to emissions failure. For example, when intake timing or undesirable scavenging occurs, thereby affecting engine performance, the occurrence of cam phasing during mid-range may affect engine performance. Furthermore, even if preloaded in a radial direction, systems known in the art may cause vibrations due to the presence of movable parts, which may cause unnecessary noise.

Thus, there is a need for a mechanical cam phasing system that can be implemented even in compact IC engines, and which should be able to perform its function only at the desired engine speeds and should be able to overcome the above-described and other problems of the prior art.

Accordingly, the present subject matter provides an internal combustion engine provided with a mechanical phasing system/assembly that uses mechanical components and that does not require external control in terms of engine speed/RPM.

The present subject matter provides a camshaft assembly including a mechanical phasing assembly capable of performing phase shifting of one of an intake lobe or an exhaust lobe relative to each other to advance/retard valve opening/closing.

The camshaft assembly of the present subject matter is capable of opening/closing the intake and exhaust valves by providing a phase shifted integrated member.

In one embodiment, a camshaft assembly includes a first cam portion and a second cam portion, wherein one or more bearings rotatably support the first cam portion and the second cam portion. Further, in one embodiment, another bearing (e.g., a roller bearing) is disposed between the first cam portion and the second portion to enable relative rotation thereof.

The intake flange is connected to one of the first and second cam portions, and the exhaust flange is connected to the other of the first and second cam portions. The terms "inlet flange" and "exhaust flange" are not limited to a single component and may include more than one flange. The camshaft assembly includes one or more cam lobes corresponding to each of the flanges, wherein the cam lobes are selected to perform valve lift according to engine requirements. Similarly, the term cam lobe refers to any geometric shape of the profile of the component performing valve actuation.

The camshaft assembly includes a driven sprocket supported on one of the cam portions. In other words, the driven sprocket is fixed to one of the cam portions. The mechanical phasing assembly includes a mass member capable of changing position in a radial direction as a function of rotational speed of the camshaft assembly. The mass member is disposed adjacent to one of the intake flange or the exhaust flange.

In one embodiment, the mass member may be formed of two or more arc-shaped members split in the circumferential direction and held close to the axis by a tension elastic member. Such two or more arc-like members are capable of moving in a radial direction due to centrifugal force.

In one embodiment, the two or more arcuate members are provided with one or more apertures and one or more pins are configured to pass through the apertures, wherein the one or more pins are movable with the arcuate members.

According to one embodiment, the intake flange, the exhaust flange and the driven sprocket are provided with elongated slots. According to one embodiment, one of the intake flange and the exhaust flange is fixed to the driven sprocket. One of the flange and the driven sprocket each has an elongated slot thereon having a phase angle or arc. The other of the intake flange and the exhaust flange has an elongated slot extending in a substantially radial direction. Thus, as the pin moves along the angled elongated slot of the driven sprocket and one flange connected to the driven sprocket, the pin shifts phase toward the other flange due to the angular movement of the pin.

For example, to phase shift the intake flange (change intake valve opening/closing according to speed), the driven sprocket and the exhaust flange are provided with arcuate elongated slots, and the intake flange is provided with substantially radially extending elongated slots. Thus, as the mass expands in the radial direction, the pin moving with the mass moves along the arcuate elongated slot that phase shifts the intake flange.

The phase shifting assembly includes an axial load member disposed substantially adjacent one of the rims. The axial load member is preloaded in an axial direction to apply a friction force to the mass member.

In one embodiment, a driven sprocket driven by the crankshaft is connected to one of the flanges, while the other flange is adapted to perform a phase shift relative to the orientation of the driven sprocket. In another embodiment, both flanges are adapted to undergo a phase shift (advance or retard) relative to the driven sprocket one at a time or two at a time.

In one embodiment, an axial load member is provided on one axial side of the driven sprocket, and the axial load member is provided with a preload in the axial direction to apply a force to the mass member. In one embodiment, a fixed member is provided on the other side of the driven sprocket and the fixed plate supports one end of the preload member, which is the other side that abuts the axial load member.

An axial load member applying a force in an axial direction causes a friction force to act on the mass member from either side. The friction balances the force components acting on the mass member in the direction of movement of the pin along the elongated slot. This force component, which would otherwise tend to move the pin in a radially outward direction, is balanced by the frictional forces exerted by the axial load members.

Thus, even when the phase angle increases to about 20 degrees, the pin tends not to slip due to friction (even if a tangential velocity component acts on the pin). It is a feature of the inventive subject matter that the camshaft assembly may be adapted to phase in the range of approximately 5-25 degrees by adjusting only the preload on the axial load member. For example, the assembly may remain unchanged and only the spring-like preload member may be replaced.

Preferably, at least two apertures are provided on the mass member, at least two elongated slots on the flange and the driven sprocket, and correspondingly, two pins are used to evenly transfer rotational force from one component to the other. Furthermore, the use of an elongated slot reduces the weight of the system and maintains the structural integrity of the components.

Furthermore, the subject matter of the invention is compactly accommodated in the axial direction. For example, in one embodiment, the driven sprocket is provided with a disc-shaped groove, and the axial load member is compactly accommodated at the groove. Therefore, no modifications to the layout, particularly the reference cam lobes and the driven sprocket, are required.

In addition, the axial load member suppresses any vibrations that may occur due to the mass member being formed of sub-members connected by tension springs.

In another embodiment, the mass member may be a collection of annularly arranged roller bearings, and the roller bearings may be movable in a radial direction due to centrifugal force applied thereto. Movement of the roller bearing in a radial direction (along a path angularly disposed on one of the contact portions) enables phase shifting. The axial load member is configured to apply an axial load that introduces frictional force to the mass member.

Various features and embodiments of the inventive subject matter will become apparent from the following additional description of the inventive subject matter set forth herein. According to one embodiment, the internal combustion engine (IC) described herein is one or the only prime mover of a motor vehicle. The IC engine may be of a forward tilting type or substantially horizontal type fixedly mounted or swingably connected to the motor vehicle. The IC engine contains at least two valves per cylinder head, one intake valve and one exhaust valve.

The inventive subject matter, as well as all attendant embodiments and other advantages thereof, will be described in more detail using embodiments of a single cylinder IC engine in conjunction with the accompanying drawings in the following paragraphs.

Fig. 1 shows a side view of an IC engine 100 according to an embodiment of the inventive subject matter. The IC engine 100 includes a cylinder block 102 supported by a crankcase 101 of the IC engine. The cylinder block 102 defines a cylinder section where pistons may perform reciprocating movements. A cylinder head 103 is mounted to the cylinder block 102, and the cylinder head 103 serves as one end of the cylinder section. The cylinder block 102 is provided with cooling fins 106, and the cylinder head 103 may be provided with cooling fins. IC engine 100 includes a piston (not shown) that performs reciprocating motion in a cylinder portion due to a force imparted thereto by combustion of an air-fuel mixture. This reciprocating motion is converted into and transmitted to rotational motion of the crankshaft 110 by a connecting rod (not shown). Further, the cylinder head-cover 104 is mounted to the cylinder head 103. The crankcase 101 is composed of a left side crankcase and a right side crankcase. The crankcase 101 rotatably supports a crankshaft 110. In addition, an electric motor, such as a magneto assembly 111 or an integrated starter generator, is mounted to the crankshaft 110. The magneto assembly 111 is used to charge a battery (not shown) during operation. The cylinder head 103 includes intake ports 105 and exhaust ports (not shown) provided on first and second faces of the cylinder head 103. In this embodiment, the first face is the upwardly facing side and the second face is the downwardly facing side thereof. Further, the cylinder head 103 supports a camshaft assembly 200 (partially shown in fig. 2) that is capable of operating intake and exhaust valves of the IC engine 100. FIG. 2 illustrates a cross-sectional view of IC engine 100 taken along line W-W' according to an embodiment of the inventive subject matter.

IC engine 100 includes a drive gear 113 connected to crankshaft 110 and rotates integrally therewith. The drive gear 113 serves as a main drive and is capable of transmitting rotational force to the main drive 112. The main driven gear 112 is thus operatively connected to the crankshaft 110. The cylinder head 103 includes a valve train arrangement for controlling the opening and closing of the intake and exhaust valves, thereby controlling the air-fuel mixture and the exhaust of the intake and exhaust gases. A camshaft assembly 200 (partially shown) is rotatably mounted to the cylinder head 103. Cam chain 114 operatively connects crankshaft 110 and camshaft assembly 200. The driven sprocket 205 of the camshaft assembly 200 is configured to engage with the drive gear 113, and the driven sprocket 205 transmits the rotational motion of the crankshaft 110 to the camshaft assembly 200. In one embodiment, the ratio of driven sprocket 205 to drive gear 113 is 2, whereby for every two rotations of crankshaft 110, camshaft assembly 200 will rotate once. IC engine 100 is provided with one or more chain tighteners 115 capable of adjusting the tension of cam chain 114 via adjustment member 116.

Fig. 3 (a) shows an isometric view of a camshaft assembly according to an embodiment of the inventive subject matter. Fig. 3 (b) shows another perspective view of the camshaft assembly with selected parts thereon according to the embodiment of fig. 3 (a). Fig. 3 (c) shows a radial cross-sectional view of camshaft assembly 200 taken along axis U-U'. The camshaft assembly 200 includes at least one intake lobe 210 and at least one exhaust lobe 211. The cam chain 114 is loaded around the drive gear 113 and the driven sprocket 205. The camshaft assembly 200 is rotatably supported by one or more bearings 215, 216. In the present embodiment, the camshaft assembly 200 includes a first cam portion 201 and a second cam portion 202. Further, the driven sprocket 205 is provided around the rotation axis of the aforementioned member. Camshaft assembly 200 includes a mechanical phasing assembly 230. The camshaft assembly 200 includes at least one intake flange 220 corresponding to the at least one intake lobe 210 and at least one exhaust flange 225 corresponding to the at least one exhaust lobe 211. In the present embodiment, the intake flange 220 is disposed between the mass member 235 and the exhaust flange 225.

In one embodiment, the camshaft assembly 200 is also provided with a pressure relief system 280. The relief system 280 includes a relief arm that pivots at one end and has a movable end. The pressure relief arm is supported on the exhaust flange 225 by a preloaded resilient member. The depressurization system 280 enables the exhaust valve to have additional lift during the compression stroke during engine start and the additional lift is reduced once the engine speed exceeds a predefined value.

Fig. 4 shows a mass member according to the embodiment of fig. 3. FIG. 5 (a) shows a cross-sectional view of exhaust cam assembly 200 taken along axis X-X' according to the embodiment depicted in FIG. 3 (a). FIG. 5 (b) shows another cross-sectional view of the exhaust cam assembly 200 taken along axis V-V' according to the embodiment as depicted in FIG. 3 (b). FIG. 6 depicts an exploded view of a camshaft assembly according to an embodiment of the present subject matter. The first cam portion 201 is rotatably supported by a first bearing 215 and has an integrally formed intake lobe 210. The first cam portion 201 extends substantially along the axis of the camshaft assembly 200 and is connected to the intake flange 220. Similarly, the second cam portion 202 has an integrally formed exhaust lobe 211 and is rotatably supported by a second bearing 216. The second cam portion 202 is at least partially coaxially disposed about the first cam portion 201. In one embodiment, a roller bearing 214 is disposed between the first cam portion 201 and the second cam portion 202. An exhaust flange 225 is supported by the second cam portion 202. The camshaft assembly 200 is rotatably supported on the cylinder head 103 (as shown in fig. 1).

In the present embodiment, the driven sprocket 205 is supported on the first cam portion 201. The driven sprocket 205 is fixed to the first cam portion 201 by a fastener 243. In addition, locking fasteners 241 (shown in FIG. 6) are provided to secure the fixed plate 240, the driven sprocket 205, and the flange 225 together. Mechanical phasing assembly 230 includes an axial load member 245. The mass member 235 is supported on the intake flange 220. Furthermore, according to the present embodiment, the axial load member 245 is disposed adjacent to the intake flange 220. The mass member 235 may be disposed adjacent to at least one of the flanges. Further, the camshaft assembly 200 includes an axial load member 245, wherein the mass member 235 is sandwiched between the axial load member 245 and the intake flange 220.

The axial load member 245 is disposed substantially on one side of the driven sprocket 205 and the fixed plate 240 is disposed on the other side of the driven sprocket 205. The driven sprocket 205 includes one or more through holes 206, and one or more axial force resilient members 242 are disposed between the axial load member 245 and the fixed plate 240 through the through holes 206, thereby providing a preload on the axial load member 245.

The driven sprocket 205 provides a rotational force received from the crankshaft 110 via one or more pins 255 (as shown in fig. 3 (b)). Such one or more pins form part of mechanical phasing assembly 230. Each of the driven sprocket 205, the intake flange 220, the exhaust flange 225 is provided with an elongated slot 260, 261, 262 and one or more pins 255 are disposed about the elongated slot 260, 261, 262 whereby rotational force from the driven sprocket 205 is transferred to the flange 220, 225 to enable rotation of the lobes 210, 211. In addition, the axial load member 245 is also provided with an elongated slot 263.

The mass member 235 is formed of a first arc member 236 and a second arc member 237, which are connected to each other by a tension elastic member 238 (as shown in fig. 4). When the centrifugal force exceeds the stiffness (k), the mass members 235 tend to expand in a radially outward direction due to the centrifugal force during rotation of the camshaft assembly 200. The resilient member 238 is selected such that after a predetermined RPM of the camshaft assembly 200, the stiffness (k) will be exceeded by centrifugal force. One of the flanges 220, 225 is provided with an angled elongated portion 261 as an arcuate portion.

The first and second arcuate members 236, 237 are provided with one or more apertures 270 through which the pins 255 pass. The movement of the arcuate members 236, 237 is guided by an elongated slot 260 provided on the driven sprocket 205. Movement of the arcuate members 236, 337 in the radial direction due to centrifugal force enables the pin 255 to move with the arcuate members 236, 237 and the pin 255 to slide through the elongated slots 260, 262, 263. However, the first elongate slot 261 is an arcuate elongate slot disposed on at least one of the ledges 225, causing the ledges 225 to shift phase due to the movement of the pins 255, thereby causing a phase shift at a desired speed/RPM relative to a second elongate slot 262 disposed on the other of the ledges 220 that extends substantially linearly in the radial direction.

In the present embodiment, the exhaust flange 225 is fixed to the driven sprocket 205 with the spacer 275 disposed therebetween. The spacer 275 can maintain a predetermined spacing between the driven sprocket 205 and the flange, thereby allowing the axial load member 245 and the mass member 235 to operate without any additional axial load from other elements. Rotation of the driven sprocket 205 rotates the exhaust flange 261, thereby maintaining the same phase. In addition, the exhaust flange 225 is provided with an angled elongated slot 261 that has a degree of movement (angular rotation) as the pin 255 slides in a radially outward direction, thereby imparting a phase shift to the intake flange 220. Accordingly, the intake lobes 210 also experience a phase shift that causes the intake valve opening/closing timing to vary. According to one embodiment, the angled elongated slots provide a phase shift in the range of 5-25 degrees. The axial load plate 245 applies an axial force to the mass member 235, whereby sliding of the arcuate members 236, 237 in the radial direction is reduced.

Fig. 7 shows an enlarged/detailed view of a cross section of a camshaft assembly 200 according to an embodiment of the inventive subject matter. When the camshaft assembly 200 is subjected to rotation, the arcuate members 236, 237 of the mass member 235 are subjected to a centrifugal force CF that tends to pull the arcuate members in a radially outward direction. The arcuate members 236, 237 are connected to each other by a resilient member 238 having a stiffness k that tends to pull the arcuate members 236, 237 in a radially inward direction with a force KF. In addition, the axial load member 245 applies an axial force to the arc members 236, 237 due to the preload acting thereon. Thus, the arcuate members 236, 237 interposed between the flange 220 and the axial load member 245 receive the frictional force FF on the mass member 235 and control premature phasing due to the stiffness/tension of the resilient member 238.

Pin 255, which is one of the primary components of mechanical phasing assembly 230 that passes through aperture 270, is also subjected to forces acting on mass member 235. Due to the torque experienced by the camshaft assembly 200, i.e., the valve train torque, this torque has a force component that acts in the direction of movement of the pin 255 along the elongated slot in the radial direction. This force component, which would otherwise tend to move the pin 255 in a radially outward direction, is balanced 245 by the frictional force exerted by the axial load member. Only when the speed/RPM of the engine 100 (which is similar to the speed of the camshaft assembly 200) is high, the centrifugal force CF replaces the force KF exerted by the elastic member 238 and the frictional force FF acting on the arc members 236, 237, whereby the arc members 236, 237 move in the radially outward direction. Thus, movement of the pin 255 changes the orientation of the flange 220, resulting in a phase shift. Further, the roller bearing 214 provided between the inner periphery of the second cam portion 202 and the outer periphery of the first cam portion 201 facilitates relative rotation between the cam portions 201, 202 during phase shifting. Thus, mechanical phasing component 230 in accordance with the present subject matter occurs in accordance with the method defined by equation (1) below. The method of mechanical phasing as detailed in fig. 8 according to the inventive subject matter is detailed below:

CF＝KF+μ(FF)………………(1)

according to one embodiment, an axial load member 245 preloaded in an axial direction configured to apply an axial load in the camshaft assembly 200 applies a resistive/frictional force FF to a side surface of the mass member 235. The axial load member 245 provides a friction force FF (which is the inherent surface friction of the material or the coefficient of friction due to a surface coating disposed on the axial load member 245) that is dependent on the coefficient of friction μ of the axial load member 245 to resist any excessive centrifugal forces acting on the mass member 235 during certain operating conditions (like sudden acceleration, etc.).

The method provides that at step S301, the system operating without any external control as a mechanical phasing system requires that the IC engine 100 be in an operating state, whereby the crankshaft rotates the camshaft assembly 200. Due to the rotation of the camshaft assembly 200, centrifugal force acts on the mass member 235 preloaded in the radial direction. Further, at step S302, the centrifugal force CF acting on the mass member 235 is checked. The term "inspection" as used herein is meant only to explain the method and does not require an actual inspection, as the mechanical phasing component 230 occurs automatically. Further, the centrifugal force CF acting on the mass member 235 is compared with the force KF exerted by the elastic member and the friction force FF according to the friction coefficient. If the centrifugal force CF is less than the accumulated force of the stiffness force KF and the friction force (i.e., μ time FF), the system returns to step S302 to continue checking the centrifugal force CF. At step S303, if the centrifugal force CF exceeds the sum of the force KF and the friction force μ time FF, then at step S304 the system performs mechanical phasing, which is performed without any external control. This results in a change in the opening and closing times of the valves to meet the intake and exhaust demands of the engine at all operating speeds.

Further, according to the present embodiment, the axial load member 245 is a disc-shaped member provided adjacent to the driven sprocket 205. Further, the axial face of the driven sprocket 205 is provided with a disc-shaped groove capable of accommodating the axial load member 245 at the groove. Thus, the axial load member 245 has a first axially inner surface 246 and the driven sprocket 205 has a second axially inner surface 207, and the first and second axially inner surfaces 246, 207 are disposed along a plane P taken normal to the axis A-A' of the camshaft assembly 200. Thus, the axial load member 245 is accommodated in the same amount of space required to accommodate the driven sprocket 205. This eliminates the need for additional mounting space on the camshaft assembly 200, particularly the space between the driven sprocket and cam lobes 210, 211. Because the position of the cam chain 114 connected to the crankshaft, the accommodation space of the cam chain 114 and the position of the valves interacting with the cam lobes 210, 211 do not need to be changed according to the inventive subject matter, in order to maintain a usable layout of the IC engine, in particular the cylinder head. Accordingly, the present subject matter provides an improved valve timing assembly/mechanical phasing assembly that does not require any layout modifications.

In one embodiment, the axial face of the axial load member 245 facing the mass member 235 and the axial face of the flange 220 facing the mass member are machined or provided with a surface coating to achieve a desired coefficient of friction.

Many modifications and variations of the present subject matter are possible in light of the above disclosure. Therefore, within the scope of the claims of the inventive subject matter, the present disclosure may be practiced other than as specifically described.

List of reference numerals

100 engine 240 fixing plate

101 crankcase 241 locking fastener

102 cylinder 242 axial force elastic member

103 cylinder head 243 fastener

104 cylinder head-cover 245 axial load member

105 air inlet 246 first axially inner surface

110 crankshaft 255 pin

111 magneto component 260-

113 drive gear 261-

114 cam chain 262-

115 chain tightener 263 elongated slot

116 adjustment member 270 orifice

200 camshaft assembly 275 spacer

201 first cam portion 280 depressurization system

202 second cam portion

205 driven gear/cam sprocket

206 holes

207 second axial inner surface

210 intake lobe

211 exhaust lobe

214

215/

216/bearing

220 air inlet flange

225 exhaust flange

230 phasing assembly

235 mass member

236 first arcuate member

237 second arcuate member

238 tension elastic member

Claims

1. An internal combustion engine (100), the internal combustion engine (100) comprising:

a cylinder block (102);

at least one piston slidably movable within a cylinder portion defined by the cylinder block (102);

a cylinder head (103), the cylinder head (103) forming one end of the cylinder section, the cylinder head (103) supporting one or more intake valves and one or more exhaust valves;

-a crankshaft (110), the crankshaft (110) being connected to the at least one piston by a connecting rod, the crankshaft (110) being rotatably supported by a crankcase (101) of the internal combustion engine (100); and

a camshaft assembly (200), the camshaft assembly (200) being rotatably supported by the cylinder head (103), the camshaft assembly (200) including a driven sprocket (205), and the camshaft assembly (200) being connected to the crankshaft (110) by the driven sprocket (205), the camshaft assembly (200) comprising:

a first cam portion (201) and a second cam portion (202);

at least one intake flange (220) and at least one exhaust flange (225), the at least one intake flange (220) being connected to one of the first cam portion (201) and the second cam portion (202), and the at least one exhaust flange (225) being connected to the remaining one of the first cam portion (201) and the second cam portion (202);

-a mechanical phasing assembly (230), the mechanical phasing assembly (230) being arranged adjacent to one of the at least one intake flange (220) and the at least one exhaust flange (225), the mechanical phasing assembly (230) comprising at least one radially preloaded mass member (235), the mass member (235) being configured to perform a phase shift of at least one of the at least one intake flange (220) and the at least one exhaust flange (225), the phase shift being generated relative to the driven sprocket (205) as a function of a rotational speed of the camshaft assembly (200), and

an axial load member (245), the axial load member (245) being preloaded in an axial direction and configured to apply an axial load.

2. The internal combustion engine (100) of claim 1, wherein the axial load member (245) is disposed adjacent to the mass member (235) for applying the axial load.

3. The internal combustion engine (100) of claim 1, wherein the camshaft assembly (200) includes a fixed plate (240), the fixed plate (240) is disposed at an axial end of the camshaft assembly (200) and adjacent the driven sprocket (205), and one or more axial force resilient members (242) are configured to apply an axial force to the axial load member (245), the one or more axial force resilient members (242) disposed between the axial load member (245) and the fixed plate (240) through one or more apertures (206) of the driven sprocket (205).

4. The internal combustion engine (100) of claim 1, wherein the driven sprocket (205) is fixed to one of the at least one intake flange (220) and the at least one exhaust flange (225).

5. The internal combustion engine (100) of claim 3, wherein the camshaft assembly (200) includes at least one intake lobe (210) connected to the corresponding at least one intake flange (220) and at least one exhaust lobe (211) connected to the corresponding at least one exhaust flange (225), and the at least one intake lobe (210) and the at least one exhaust lobe (211) are adapted to control opening and closing of the one or more intake valves and the one or more exhaust valves, and the at least one intake lobe (210) and the at least one exhaust lobe (211) are disposed on one side of the axial load member (245) and the fixed plate (240) is disposed on the other side of the axial load member (245).

6. The internal combustion engine (100) of claim 1, wherein the axial load member (245) is a disc-shaped member disposed adjacent to the driven sprocket (205), and wherein the driven sprocket (205) is provided with a disc-shaped recess configured to receive the axial load member (245) therein.

7. The internal combustion engine (100) of claim 1, wherein the axial load member (245) has a first axially inner surface (246) and the driven sprocket (205) has a second axially inner surface (207), and the first axially inner surface (246) and the second axially inner surface (207) are disposed along a plane (P) taken normal to an axis (A-A') of the camshaft assembly (200).

8. The internal combustion engine (100) of claim 1, wherein the mechanical phasing assembly (230) comprises one or more pins (255) extending in the axial direction and disposed through one or more elongate slots (260, 261, 262, 263) disposed on the driven sprocket (205), on the at least one intake flange (220), on the at least one exhaust flange (225), and on the axial load member (245), wherein the one or more elongate slots (260, 261, 262, 263) comprise angled elongate slots (261).

9. The internal combustion engine (100) of claim 1, wherein the mass member (235) is formed of two or more arcuate members (236, 237) connected to each other by one or more tension elastic members (238), and the two or more arcuate members (236, 237) are in frictional contact with the axial load member (245), and a spacer (275) is provided between the driven sprocket (205) and the at least one of the at least one intake flange (220) and the at least one exhaust flange (225) to maintain a predetermined spacing.

10. The internal combustion engine (100) of claim 9, wherein the mass member (235) is formed by a first arcuate member (236) and a second arcuate member (237) forming two or more arcuate members (236, 237), the two or more arcuate members (236, 237) being provided with one or more apertures (270) for receiving the one or more pins (255) through the one or more apertures (270), the one or more pins (255) passing through the one or more elongated slots (261, 262) provided on the at least one intake flange (220) and the at least one exhaust flange (225) to create the phase shift between the at least one intake flange and the at least one exhaust flange to result in variable valve timing control.

11. The internal combustion engine (100) of claim 10, wherein the one or more elongated slots (261, 262) include a first elongated slot (261) and a second elongated slot (262), the first elongated slot (261) being disposed on one of the at least one intake flange (220) and the at least one exhaust flange (225) extending in an arcuate manner in an axial direction, the second elongated slot (262) being disposed on the other of the at least one intake flange (220) and the at least one exhaust flange (225) extending substantially in a linear-axial direction.

12. A motor vehicle comprising an internal combustion engine (100) according to any one of claims 1-11.

13. A camshaft assembly (200), the camshaft assembly (200) configured to be rotatably supported on a cylinder head (103) of an internal combustion engine (100), the camshaft assembly (200) comprising:

a driven sprocket (205);

two or more cam portions (201, 202);

at least one air intake flange (220), the at least one air intake flange (220) being connected to at least one of the two or more cam portions (201, 202); and

at least one exhaust flange (225), the at least one exhaust flange (225) being connected to at least one other of the two or more cam portions (202);

-a mechanical phasing assembly (230), the mechanical phasing assembly (230) being configured to perform a phase shift of at least one of the at least one intake flange (220) and the at least one exhaust flange (225) relative to the driven sprocket (205) in accordance with a rotational speed of the camshaft assembly (200); and

-an axial load member (245), the axial load member (245) being preloaded in an axial direction for applying an axial load.

14. A method of operating a mechanical phasing assembly (230) for a camshaft assembly (200) of an internal combustion engine (100), the method comprising the steps of:

checking a Centrifugal Force (CF) acting on a mass member (235) of the camshaft assembly (200);

comparing the Centrifugal Force (CF) with a cumulative force, the cumulative force being a sum comprising a rigid force (FF) exerted by the tension elastic member (238) and a friction force (μ (FF)) exerted by the axial load member (245); and

mechanical phasing is performed by the mechanical phasing assembly (230) when the Centrifugal Force (CF) exceeds the cumulative force.